So, a couple things here. In the presser, OZ stated that the reason this deal got done was because both Joe and Steve wanted it to happen. It had less to do with cap space, and Oz reinforced that they were prepared to go either route. The cap savings is great, it helps both sides, but it wasn't the end-all be-all for the contract.
As for Brady. Well, his wife is worth 3-4x as much as he is. He can afford to take these extensions every year or two and he's still getting GTD monies with the lower cap hits. He has also had a couple sizable contracts, and will be playing into his 40s. He's a poor example. Guys like Cutler, Wilson, Rodgers, etc are better examples of the market value.